fs/ntfs3: Fix a possible null-pointer dereference in ni_clear()

In the Linux kernel, the following vulnerability has been resolved: fs/ntfs3: Fix a possible null-pointer dereference in ni_clear() In a previous commit c1006bd13146, ni->mi.mrec in ni_write_inode() could be NULL, and thus a NULL check is added for this variable. However, in the same call stack, ni->mi.mrec can be also dereferenced in ni_clear(): ntfs_evict_inode(inode) ni_write_inode(inode, ...) ni = ntfs_i(inode); is_rec_inuse(ni->mi.mrec) -> Add a NULL check by previous commit ni_clear(ntfs_i(inode)) is_rec_inuse(ni->mi.mrec) -> No check Thus, a possible null-pointer dereference may exist in ni_clear(). To fix it, a NULL check is added in this function.